The present invention relates to improvements in automatic arc welding processes, and more particularly the invention relates to an improved method of multiple electrode gas shielded arc welding.
The gas shielded arc welding process is one of the automatic arc welding process. In this process, generally a pure gas such as pure argon or pure carbon dioxide gas or a mixed gas comprising mainly argon and a small addition of oxygen or carbon dioxide gas is used to prevent access to oxygen and nitrogen and in this way the arc welding is accomplished. While this process has the advantage of low welding input heat and hence welded joint metals of excellent properties as compared to other arc welding processes such as the submerged arc welding process, it has the disadvantage of low welding efficiency. In view of this fact, a welding method has been used in which two or more electrode wires of the same chemical composition are arranged along the welding seam line of a piece to be welded and the weld metal is continuously deposited in a series of layers by the plurality of electrodes, thereby ensuring an improved welding efficiency. While this method has the effect of considerably improving the welding efficiency, it is also disadvantageous in that the chemical composition of the weld metal made by each of the respective passes such as the first and second passes differ from one another and consequently there results a wide variation in the properties, particularly the impact property of the weld metal at the different positions in the entire weld metal corresponding to the passes, thus making it difficult to obtain a homogeneous weld zone.